libimage_io: Add host_supported flag to builds.

Bug: 207411352
Test: Built libimage_io host build.
Change-Id: Ic17572fb3dc0f0de23e3bfd89d27337d54110bcb

Android.bp

diff --git a/Android.bp b/Android.bp
index 8fe553e..58eaedc 100644
--- a/Android.bp
+++ b/Android.bp
@@ -36,12 +36,14 @@
 
 cc_library_headers {
   name: "libimage_io-headers",
+  host_supported: true,
   export_include_dirs: ["includes"],
 }
 
 
 cc_library {
     name: "libimage_io",
+    host_supported: true,
     defaults: ["libimage_io-defaults"],
     header_libs: ["libimage_io-headers"],
     export_include_dirs: ["includes"],